Corrugated boards are generally produced on an automated line in which web guiding systems are commonly used to correctly guide and tension the material on the web. Since the board material which is guided in web form is generally thin, there is a tendency for the material to wander from its correct alignment on the web. Other factors, such as material irregularity, web speed or faulty machinery, are also liable to lead to a percentage of the manufactured boards being sub-standard. Generally, these sub-standard boards are removed during the production process. Generally, the corrugated boards are stacked in piles of several hundred, commonly 400 boards per stack.
Reference is now made to FIG. 1 which illustrates three stacks, designated 10A, 10B and 10C, of manufactured boards 12 being conveyed together along the corrugated board production line, generally designated 1. Each of the stacks contains a plurality of corrugated boards 12, laid one on top of each other. In the typical example, shown in FIG. 1, stack 10A contains more boards than stack 10B and stack 10C contains more boards than 10A.
An enlarged detail of the top of stacks 10A and 10B is shown in FIG. 2, to which reference is now made. The top rows of the corrugated boards are referenced 14, 16, 18 and 20 in stack 10A, and 22 and 24 in stack 10B. Stack 10A contains two extra boards, 14 and 16. Boards 18 and 20 of stack 10A are aligned with boards 22 and 24 of stack 10B.
During manufacture, the width of the boards may vary, as exaggerately illustrated in FIG. 2, so that board 16 is narrower than boards 14 and 18, for example.
The depth of each corrugated board may vary so that it is not possible to measure the total height of a stack in order to calculate the number of boards contained therein.
Since sub-standard boards are removed during the production process from any or all of the stacks, the final number of boards in each stack will vary and furthermore, the manufacturer cannot easily determine their number. Since the purchaser is paying for a stack of 400, say, any shortfall is made up by the manufacturer. Usually, manufacturers add 10-20 extra boards to each pack to satisfy the purchaser. This over-compensation by the manufacturer is inefficient and costly.
The applicant has realized that since each corrugated board has a characteristic but distinctive "wave corrugation", it is possible to determine the number of boards in a stack by counting the number of "wave corrugations". One possible system, illustrated in FIG. 3, utilizes a camera 30 together with a parabolic reflector 32 to "scan" a stack 34 of corrugated boards 36. However, it was found that in order to scan the whole stack, the camera has to be placed far away from the stack. The resultant resolution was too low to accurately determine the number of boards.
An alternative configuration used a plurality of cameras, each of which scanned a portion of the stack. For example, it was found that to obtain a high enough resolution, each camera could only scan 40 boards. Since, the standard stack contains approximately 400 boards, ten cameras would be needed. In addition to being costly, it is difficult to ascertain where each camera begins and ends its "scan". To overcome the problem of scan overlap, a "laser" pointer is additionally required.
The previous embodiments have the further disadvantage in that the line must be stationary at the time the scan takes place.